JPH0582302B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal head, and in particular, to a thermal head that provides good contact between the thermal head and an ink film or thermal coloring paper, and provides an optimal temperature distribution on the surface of the head. The present invention also relates to a thermal head that has high thermal responsiveness and is suitable for obtaining high-speed, high-definition, and high-quality printing.

[Background of the invention]

In general, a thermal head, as shown in FIG.
A heat storage layer 2 is provided on a substrate 1 made of ceramic or the like, and a minute heating resistor 3 is provided on the surface of this heat storage layer 2.
There are multiple locations. Each of these heating resistors is provided with an electrode 4 for power supply. 5 is a protective layer consisting of two layers: an oxidation-resistant layer for preventing oxidation of the heating resistor 3 and the electrode 4, and an abrasion-resistant layer for preventing wear of this oxidation-resistant layer. Note that depending on the material of the protective layer, one material may serve as both the oxidation-resistant layer and the wear-resistant layer, and in this case, the protective layer is one layer.

In the printing mechanism of a thermal printer equipped with this thermal head, when power is supplied to the heating resistor 3 through the electrode 4, heat is generated in the heating portion 3a of the heating resistor 3, and this heat passes through the protective layer 5 and then reaches the head. The ink is transmitted from the printing dot portion 6a on the surface 6 to an ink film and an ink layer (not shown), and the ink in the ink layer is melted and attached to a recording medium (not shown) such as printing paper to print. Alternatively, the color is transferred to a coloring layer of heat-sensitive coloring paper (not shown) to develop color and print. When printing is completed, the power supply to the heating resistor 3 is cut off, and after it has cooled sufficiently to the point that no printing occurs, the relative position of the thermal head and the recording medium is shifted to the next printing position (usually by one dot). position) and repeat the above series of printing operations.

Therefore, in order to achieve high-speed printing, the head must have high thermal responsiveness, that is, the heating resistor 3
The heat generated in the heat generating part 3a is quickly transferred to the printing dot part 6a, and the temperature of the dot part 6a is the temperature necessary to melt the ink layer (not shown) or color the thermosensitive coloring paper. It is necessary to raise the temperature to a high temperature and then quickly cool it down. Furthermore, from the viewpoint of printing quality, it is desirable that only the temperature of the printing dot section 6a above the heat generating section 3a rises uniformly, and the temperature of the surrounding head surface 6 including the adjacent dot sections does not change.

Generally, the print density is determined by the print dot portion 6a.
It largely depends on the contact pressure between the ink film or the heat-sensitive coloring paper, and the relationship is as shown in FIG. 2. Therefore, the shape of the heat-sensitive head surface 6 shown in FIG. 1 requires that the distribution of the contact pressure between the printing dot portion 6a and the ink film or heat-sensitive coloring paper be uniform at least within the printing dot portion 6a. be.

By the way, in the conventional thermal head, as shown in FIG. 1, the printing dot portion 6a is one step lower than the head surface 6. Therefore, the state of contact between the printing dot portion 6a and the ink film or heat-sensitive coloring paper 9 is as shown in FIG. 3a,
At that time, the pressure distribution was as shown in FIG. 3b, and the pressure was not uniform on the printed dot portion 6a. In particular, within the printing dot part 6a, which is extremely important for printing quality, the pressure decreases as it goes outward.
Particularly, at the end of the printed dot portion 6a, a gap 10 is created between the printed dot portion 6a on the surface of the head and the ink film or heat-sensitive coloring paper 9. As a result, the area of the printed dots was smaller than the area of the printed dot portion 6a, and furthermore, the dots around the printed dots were not clearly visible. Furthermore, due to the mechanism in which printing is repeated while the thermal head and the ink film or the thermal coloring paper 9 move relative to each other, fluctuations in the pressing force between the head and the ink film or the thermal coloring paper are unavoidable. This variation in pressing force causes a variation in the size of the gap 10 between the print dot portion 6a of the head and the ink film or heat-sensitive coloring paper 9, that is, a variation in the size of the print dot, resulting in a decrease in image quality. It was bringing about. Furthermore, due to the poor contact condition between the printing dot part 6a of the thermal head and the ink film or thermal coloring paper as described above, the contact thermal resistance between the two becomes large, and the printing dot part 6a and the ink There was a large temperature difference between the film and the thermosensitive coloring paper 9. Therefore, in order to melt the ink in the ink layer (not shown) on the ink film or to color the thermosensitive coloring paper, it is necessary to raise the temperature of the printed dot portion 6a to an extremely high temperature. Further, the heat generated in the heat generating portion 3a of the heat generating resistor 3 shown in FIG. Since the contact heat resistance between the dots and the dots is large, the heat is propagated to the surroundings, increasing the temperature of the head surface 6 around the dots, including the adjacent print dots 6a, and causing the cuts in the print dots to become obvious. Otherwise, the printing dots would spread out, leading to deterioration in printing quality.

By increasing the pressing force between the heat-sensitive head and the ink film or heat-sensitive coloring paper 9, the various drawbacks mentioned above can be improved to some extent, but the abrasion of the protective layer 5 becomes severe and the life of the head is shortened. Also, if the pressing force is too large, the ink may be transferred to the paper or the heat-sensitive coloring paper may develop color even though no heat is applied, a phenomenon called pressure transfer or pressure coloring. A phenomenon occurs. Therefore, in the conventional structure,
There is no fundamental solution to the various drawbacks mentioned above.

Therefore, Japanese Patent Publication No. 55-30408 discloses an invention in which the above-mentioned drawbacks are improved by using a retreating electrode to improve the contact between the printed dots and the ink film or heat-sensitive coloring paper.
Furthermore, although there is a thermal pen, Japanese Utility Model Publication No. 13703/1983 discloses one in which the printing dot part is made of diamond and the diamond is made to protrude beyond the surface of the head.
However, in the former structure, although the dents of the printed dots on the head surface are considerably improved compared to the conventional structure, the dents still exist, and the above drawbacks have not been completely solved. Also, in the latter structure,
The contact pressure gradient within the printed dot is rather large compared to the conventional structure, and the contact area between the printed dot and the ink film or heated coloring paper varies greatly depending on the pressing force of both, which again results in the various drawbacks mentioned above. It's hard to say it's a fundamental solution.

Furthermore, in the conventional heat-sensitive head, the protective layer 5 is made of a material with a poor temperature conductivity K of about 10 ^-2 to ^{10 -3} cm ² /S (for example, SiO ₂ , Ta ₂ O ₅ , etc.). In addition, in order to withstand wear and to play a role in preventing oxidation of the heating resistor 3 and the electrode 4, the thickness thereof is also formed to be uniform and about 5 to 10 μm. Therefore, the heating portion 3 of the heating resistor 3
The thermal resistance between the heat generating part 3a and the printed dot part 6a on the head surface 6 became very large, and a large temperature difference was generated between the heat generating part 3a and the printed dot part 6a. Therefore, in order to raise the temperature of the printing dot portion 6a on the surface of the head to the temperature required for printing, it is necessary to raise the temperature of the heat generating portion 3a extremely high. In order to perform high-speed printing with such a heat-sensitive head, it is necessary to raise the temperature of the print dot portion 6a on the head surface to a predetermined temperature within a short period of time, so the input power to the heating resistor 3 increases. Heat generating resistor 3
The temperature of the print head was higher than when printing at low speeds, which could damage the head, and it also naturally took time to cool down after the input power was cut off, putting a limit on how fast printing could be done. .

Furthermore, since the thermal resistance from the heat generating portion 3a of the heat generating resistor 3 to the printed dot portion 6a on the head surface 6 is large, a large amount of heat escapes to the surroundings, and the heat generating resistor 3
Another drawback was that most of the input power to the printer was not used for printing.

[Purpose of the invention]

The purpose of the present invention is to provide uniform and smooth contact pressure between the head and the ink film or heat-sensitive coloring paper, to provide the head surface with a temperature distribution suitable for printing quality, and to enable high-quality, high-definition printing. The object of the present invention is to provide a heat-sensitive head that is

[Summary of the invention]

In the thermal head of the present invention, a thermally conductive material having a higher temperature conductivity than the protective layer is provided on the portion of the protective layer corresponding to the heat generating portion so that the surface of the head is flat, so that the print dot portion on the surface of the head is flat. Improve the contact between the head and the ink film or heat-sensitive coloring paper, make the contact pressure between the two uniform within the printing dot area, reduce uneven print density and fluctuations in dot area, and improve printing quality. By reducing the thermal resistance from the heating part of the heating resistor to the ink film or thermal coloring paper through the printed dots on the head surface, the heat generated in the heating part of the heating resistor is quickly transferred to the head surface without escaping to the surroundings. The heat reaches the printed dots and then the ink film or heat-sensitive coloring paper, and conversely, when it cools down, the heat is quickly radiated, and the heat reaches the heat-generating part of the heating resistor, the print dots on the head surface, and the head surface and the ink film or heat-sensitive coloring paper. It is characterized by a small temperature difference between it and the colored paper.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. The same reference numerals as in FIG. 1 indicate the same parts. Reference numeral 7 denotes an electrically insulating heat conducting member, which is provided for each heating dot only in the portion of the protective layer 5 corresponding to the heating portion 3a of the heating resistor 3. One surface is in thermal contact with the heat generating portion 3a, and the other surface is exposed to the head surface 6, forming a printing dot portion 6a that is flat with the head surface 6. 6th
Figures a and b show the state of contact between the head and the ink film or heat-sensitive coloring paper and the distribution of contact pressure at that time. In this embodiment, since the head surface 6 is flat as shown in FIG.
The contact pressure distribution is almost uniform as shown in Fig. 6b, and
It will be good. Therefore, the printed dots are of high quality, high image quality, and high definition, with no density unevenness, constant size, and sharp cuts.

By the way, the heat conductive member 7 shown in FIGS. 4 and 5 is made of a material whose temperature conductivity K is at least higher than that of the protective layer 5, such as SiC, Al ₂ O ₃ , etc., whose temperature conductivity is 0.1 to 1 cm ² /S. It is made of material with a certain value. Therefore, the temperature conductivity K is 10 to 1000 times greater than that of the surrounding protective layer 5. Now, the distance that heat propagates during time t is proportional to kt, so the distance that heat travels in the same time is 3
~30 times larger. Therefore, during heating, heat from the heat generating portion 3a of the heat generating resistor 3 is quickly transferred to the head surface 6.
The heat is transmitted to the printing dot portion 6a, and on the contrary, the heat is quickly dissipated during cooling, so high-speed printing is possible.

In addition, the temperature difference between the heat generating part 3a of the heating resistor 3 and the printing dot part 6a on the head surface is small, and the escape of heat to the surroundings is also small. Since the dot portion 6a has no dents and is flat, it makes good contact with the ink film or the heat-sensitive coloring paper 9. Therefore, the contact thermal resistance between the head surface 6 and the ink film or heat-sensitive coloring paper 9 is reduced, so that the input power to the heating resistor 3 can be significantly reduced. This is nothing but a reduction in the amount of heat generated in the heat generating portion 3a, and therefore the time required for cooling can be shortened, so that high-speed printing is also possible. Furthermore, since the heat dissipation from the heat conductive member 7 to the surrounding protective layer 5 is small, the temperature of the head surface 6 increases only at the printing dot portion 6a formed by the heat conductive member 7, There is almost no rise in the surrounding area. Therefore, since each printed dot on the head surface 6 has high thermal independence and high thermal conductivity, the temperature of the printed dot portion 6a becomes almost uniform, resulting in a sharp density at the cut. Even printing is possible and high print quality can be obtained.

7 to 15 show other embodiments of the thermal head of the present invention, and the same reference numerals as in FIGS. 4 and 5 indicate the same parts.

In the embodiment shown in FIGS. 7 to 11, the shape of the heat conductive member 7 is formed such that the surface area of the side 7a that contacts the heat generating part 3a is larger than the surface area of the printed dot part 6a side 7b. , Figures 7 and 8
In the example shown in the figure, the shape of the heat conductive member 7 is changed in stages, and in the example shown in FIGS. 9 and 10, the shape of the heat conductive member 7 is
This is an example in which the shape of is continuously changed. With this configuration, in addition to having the effect of the embodiment shown in FIG. 2, the heat reaches the printing dot portion 6a through the inside of the heat conduction member 7, so there is no need to worry about the shape and size of the heat generating portion 3a. The shape and dimensions of the printed dot portion 6a can be determined without any problems. Therefore, by reducing the size of the printing dot portion 6a, high-definition printing is possible. Conversely, since the shape and dimensions of the heat generating section 3a can be determined regardless of the shape and dimensions of the printed dot section 6a, there is also the advantage that there is some leeway in setting the resistance value or applied power of the heat generating section 3a. In addition to the shape of the heat conductive member 7 described above, the cross-sectional width of the heat conductive member 7 in the electrode direction is not changed, and only the cross-sectional width in the adjacent dot direction is changed, so that the heat generating portion 3a of the heat conductive member 7 is contacted. Naturally, the same effect can be obtained even if the surface area of the printed dot side 7a is made larger than the surface area of the printed dot portion 6a side 7b.

In the embodiment shown in FIG. 11, the cross-sectional width of the side 7a of the heat-conducting member 7 that contacts the heat generating part 3a is larger in the electrode direction than the cross-sectional width of the printed dot part 6a side 7b.
It is made smaller in the direction of adjacent dots. This embodiment provides the same effects as the previous embodiments, and also improves print quality or image quality because the gap between adjacent print dots becomes smaller.

In each of the embodiments described above, the heat conductive member 7
is placed directly on the upper surface of the heat generating part 3a and is thermally connected to the heat generating part 3a. Therefore, the heat conductive member 7 must be made of an electrically insulating material. In the embodiment shown in FIG. 12, a heat conductive member 7 is provided on the upper surface of the heat generating portion 3a via an electrically insulating member 8 formed thinner than the protective layer 5. In this case, the heat conductive member 7 may be made of a conductive material such as metal. Even if the electrical insulating member 8 is interposed between the heat generating part 3a and the heat conductive member 7 in this way, the electrical insulating member 8 is formed thinner than the protective layer 5, so the thermal resistance will not be large. First, it is possible to bring about the same effects as the structure of the embodiment shown in FIGS. 4 and 5. At this time, the shape and dimensions of the printed dot portion 6a can be arbitrarily selected by changing the shape of the heat conductive member 7 stepwise or continuously as shown in FIGS. 7 to 11.

In the embodiment shown in FIG. 12, the electrical insulating member 8 is provided only on the upper part of the heating dot part 3a of the heating resistor 3, but in the embodiment shown in FIG. After the body 3 and the electrodes 4 are coated to cover the entire body 3 and the electrodes 4, a protective layer 5 is provided, and a heat conductive member 7 is applied only to the portion corresponding to the heating dot portion 3a. With this configuration, compared to each of the embodiments described above, the electrically insulating member 8 acts as a sealing member, so that the heating resistor 3 and the electrode 4 can be oxidized through the space between the thermally conductive member 7 and the protective layer 5. The possibility of the head being damaged is extremely small, and the life expectancy of the head can be expected to be improved. At this time, since the electrical insulating member 8 is formed thinner than the protective layer 5, it does not have a large thermal resistance, and can produce the same effect as the embodiment shown in FIGS. 4 and 5. At this time, the heat conductive member 7
By changing the shape stepwise or continuously as shown in FIGS. 7 to 11, the shape and dimensions of the printed dot portion 6a can be arbitrarily selected.

Even if the electrically insulating member 8 shown in FIG. 13 is coated to cover the entire electrode 4 and thermally conductive member 7 as shown in FIG. 14, the same effect as in the example shown in FIG. 13 can be obtained. can. In this case, it is necessary to increase the thickness of the protective layer 5 by the thickness of the electrically insulating member 8 so that the head surfaces are on the same plane. Further, if the heat conductive member 7 is made of an electrically insulating material, the electrically insulating member 8 may be provided to cover the entire head surface 6a, as shown in FIG. Even with this configuration, the above-mentioned 13th
It is possible to obtain the same effect as the structure shown in FIGS. Note that in this case, the electrically insulating member 8 may be a conductive member.

〔Effect of the invention〕

As explained above, according to the present invention, the contact pressure between the head and the ink film or thermosensitive coloring paper is uniform and good, and the temperature distribution in the printing head can be improved, resulting in high quality and high definition printing. can be printed.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective sectional view of an example of a conventional thermal head, and FIG. 2 is a diagram showing the relationship between the contact pressure between the thermal head and ink film or thermal coloring paper and print density. Figures 3a and 3b are diagrams showing the state of contact between a conventional thermal head and ink film or thermal coloring paper and the contact pressure distribution at that time, and Figure 4 shows the main part of an embodiment of the thermal head of the present invention. Partially cutaway perspective sectional view, fifth
The figure is a sectional view taken along the V-V' arrow in Fig. 4, and Fig. 6 a, b.
4 and 5 are diagrams showing the state of contact between the thermal head and the ink film or thermosensitive coloring paper, and the contact pressure distribution at that time. FIGS. FIG. 2 is a partially cutaway perspective sectional view showing a main part of the embodiment. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Heat storage layer, 3... Heat generating resistor, 3a... Heat generating part of heat generating resistor, 4... Electrode,
5... Protective layer, 6... Head surface, 6a... Printed dot portion on head surface, 7... Heat conductive member, 7a
...The side that contacts the heat generating part 3a of the heat conductive member 7, 7
b...Printed dot portion 6a side of thermally conductive member 7, 8...
...Electrical insulating member, 9... Ink film or thermosensitive coloring paper.

Claims (1)

[Scope of Claims] 1. A heat storage tank, a plurality of heating resistors, an electrode provided for each heating resistor for supplying power to each heating resistor, and protection to prevent oxidation and wear of the heating resistor and electrodes. In a thermal head having a layer formed on a substrate, the printing head portion of the protective layer is made of a thermally conductive member having a higher temperature conductivity than the protective layer formed independently for each dot portion, and the printing dot portion 1. A heat-sensitive head, characterized in that the heat-conducting member has one surface disposed on the heat-generating resistor with an electrically insulating member interposed therebetween. 2. The heat-sensitive head according to claim 1, wherein the electrically insulating member is disposed to cover the joint between the protective layer and the heat-conducting member. 3. The thermal head according to claim 1, wherein the electrically insulating member is disposed to cover the electrode and the heating resistor. 4. The thermally conductive member according to any one of claims 1 to 3, wherein the surface shape on the printed dot side is different from the surface shape on the heating resistor side. Heat sensitive head. 5. The heat-sensitive head according to claim 4, wherein the heat-conducting member is formed so that its cross-sectional shape becomes gradually smaller from the heating resistor side to the printing dot side. 6. The heat-sensitive head according to claim 4, wherein the heat-conducting member is formed so that its cross-sectional shape becomes smaller continuously from the heating resistor side to the printing dot side.